The driving wheels of tracked vehicles have a plurality of teeth formed on a radially outer part of the wheel. More, recently, the track-engaging portion of the drive wheels have been formed as separate members each including a number of teeth with each of the members mounted on a flanged ring. The teeth in the segments have undercut surfaces that heretofore have been machined or flame cut to the required close-toleranced final dimension. On these segments, or better on their surfaces, a machining allowance thickness of about 3 mm is provided and 1.5 mm limits of clearance are provided to comprise a final allowance between 1.5 mm and 4.5 mm. Machining of this forged segment is extremely laborious, very expensive, and adverse results are often obtained.
The present invention is directed to overcoming and on more of the problems set forth above in addition to offering several new advantages. The inventor has found a manufacturing procedure and forging means that give a forging perfect shape and dimensions, that is to say, within the tolerance limits that are to be kept not for the forging operations but for the machining operation. In order to achieve these results, the inventor has looked at the different tolerances and has made an ideal discrimination between shapes and surfaces that have greater degrees of tolerance and forms and surfaces that have very restricted tolerances, in order to place the operations of coining on the surfaces with restricted tolerances, letting the excess of material to be located on the surfaces where greater tolerances are allowed. Following this theoretical discrimination there has corresponded the development of a coining die for forming surfaces on two planes at right angles with respect to each other and in the same phase, which allows on to coin the surfaces and move material from one surface to the other, according to a preset balance.
This is a coining or minting process that surpasses in all respects the concept of finishing with machine tools. In fact, the concept of finishing with machine tools is that of (taking the route of) removal of excess metal and its elimination under the form of shavings, a method which involves a destruction of the better part of the forging with the cutting of the forges surface and the exposure of open grains of the metal.
The present invention, instead, uses the excess material on certain surface and the deficiency of material on other surfaces for mutual compensation, leaving the eventual final excess or deficiency on the surfaces that can stand greater tolerances. That is to say that during the single phase of coining, all the surfaces within a restricted tolerance, none of them excluded, are matched by the coining surfaces and all the surfaces with larger margins of tolerance are left free to take up the excess and deficiencies resulting from the structuring brought about by the minting or coining process. In this way the forged metal flow lines and grains of the metal are left intact and the same surfaces of the forging present an outer layer which is tougher and more porous and, therefore, much better adapted to keep lubricants and to bear the mechanical wear and oxidation than those surfaces finished by machine tools. It must be taken into account that, because of the complex form of the segment and the different dislocation of the surfaces to be finished by machining, the previous process had to be carried out on two tool machines with processes of relatively complexity.